Xanthine oxidase (XOD) was extracted from bovine milk. Immobilization of extracted XOD was performed by covalently N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) chemistry on core–shell magnetic nanoparticles (MNPs)/carboxylated multiwalled carbon nanotube (c-MWCNT) composite film. The film was electrodeposited on glass plate electrode (usually the surface of fluorine doped tin oxide (FTO). In order to characterize nanocomposite modified FTO electrode, various methods including scanning electron microscopy (SEM), cyclic voltammetry (CV), Fourier transform infrared (FTIR), and electrochemical impedance spectroscopy (EIS) were performed. These methods were evaluated prior and following XOD immobilization. The working optimal conditions for instance 30 °C, +0.2 V vs. Ag/AgCl, sodium phosphate buffer at pH 7.0 were attributed for developing this biosensor. The linearity of the response upto 150 μM xanthine concentration, 0.05 μM (S/N = 3) detection limit and a response time within 3 s were obtained. The biosensor was stored at 4 °C and used above 100 times for a long period of 120 days. The loss of 50 % of activity was noticed. This fabricated biosensor was then employed determining xanthine in fish meat sample.